Omeprazole (trade name Prilosec), a specific inhibitor of the gastric proton pump (H.sup.+ +K.sup.+)-ATPase, can be prepared by coupling 2-chloromethyl-3,5-dimethyl-4-methoxypyridine and 5-methoxy-2-mercaptobenzimidazole, followed by oxidation. 2-chloromethyl-3,5-dimethyl-4-methoxypyridine, in turn, is readily obtainable by chlorination of 2-hydroxymethyl-3,5-dimethyl-4-methoxypyridine (i.e., compound 9 shown in Scheme A below).
Conventional methods of preparing compound 9 involve using either N-oxide or nitropyridine as an intermediate. E.g., see U.S. Pat. No. 4,255,431 (1981) and European Patent Application 369,208 (1990). Both N-oxide and nitropyridine have been reported to be carcinogenic.